Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

An aluminum-based casting alloy having improved corrosion resistance and
casting characteristics for sand and permanent mold casting processes.
The aluminum-based casting alloy contains from about 4.0 to about 7.0
percent silicon by weight, at least 87 percent aluminum by weight, from
about 0.25 percent to about 0.5 percent manganese by weight, a maximum of
0.08 percent copper by weight, and from about 0.2 percent to about 0.8
percent iron by weight.

Claims:

1. An aluminum-based alloy comprising:at least about 87 percent aluminum
by weight;from about 4.0 percent to about 8.5 percent silicon by
weight;from about 0.25 percent to about 0.5 percent manganese by weight;a
maximum of about 0.08 percent copper by weight; andfrom about 0.2 percent
to about 0.8 percent iron by weight.

2. The alloy of claim 2, wherein the silicon is present in an amount of
from about 4.0 to 7.0 percent by weight.

3. The alloy of claim 1, having a maximum of 0.05 percent copper by
weight.

4. The alloy of claim 1, wherein the aluminum is present in the alloy in
an amount of at least 88 percent by weight.

5. The alloy of claim 1, wherein the aluminum is present in the alloy in
an amount of at least 89 percent by weight.

6. The alloy of claim 1, wherein the manganese is present in an amount of
from about 0.3 percent to about 0.5 percent by weight.

7. An article of manufacture made from an aluminum alloy comprising:at
least about 87 percent aluminum by weight;from about 4.0 percent to about
8.5 percent silicon by weight;from about 0.25 percent to about 0.5
percent manganese by weight;a maximum of about 0.08 percent copper by
weight; andfrom about 0.2 percent to about 0.8 percent iron by weight.

Description:

TECHNICAL FIELD

[0001]This invention relates to aluminum alloys; particularly, to aluminum
casting alloys; and more particularly, to aluminum casting alloys used
for sand and permanent mold casting processes.

BACKGROUND OF THE INVENTION

[0002]Components formed from casting of known aluminum alloys may not be
sufficiently resistant to corrosion for certain automotive applications.
Aluminum automotive components that are exposed to temperature extremes,
water, snow, ice and humidity, as well as corrosion inducing materials
such as salt, and dirt and road grime that can retain moisture and salt,
eventually tend to exhibit significant corrosion.

[0003]U.S. Pat. No. 6,733,726 B2 provides for an aluminum alloy that is
suitable for die-casting components for automotive applications. The
aluminum die casting alloy is characterized by a very low copper content,
a manganese content that is sufficient to enhance the stability of the
alloy and have a positive influence on the strength properties, and a
silicon content that is sufficient to impart excellent fluidity, hot tear
resistance and feeding characteristics for good die-castability. The
aluminum die casting alloy contains about 4.5 to about 12 percent silicon
by weight, at least 87 percent aluminum by weight, about 0.25 percent to
about 0.5 percent manganese by weight, and a maximum of 0.08 percent
copper by weight. The resulting aluminum alloy has improved corrosion
resistance and excellent strength characteristics; however, the alloy is
formulated mainly for die-casting processes in which the alloy is
subjected to high gauge pressure for introducing molten alloy into the
die-cast dies.

[0004]Sand and permanent mold casting may be a more cost efficient
alternative to die-casting for forming certain components. As compared to
die-casting, both sand and permanent mold casting processes require very
low to no gauge pressure in introducing the molten aluminum alloy into
the mold. Sand casting is a process in which molten metal is poured into
a mold formed of sand under gravity or low pressure or in vacuum and held
until the alloy is cooled and solidified. Permanent mold casting is
similar to sand casting except that the mold is typically formed of a
metal that has a higher melting point than the alloy that is poured into
the mold. Components formed from sand and permanent mold casting can be
heat treated to obtain the desired mechanical properties. Components
formed from aluminum alloys designed for die casting cannot be heat
treated, and therefore requires the alloy formulation be tailored to
provide the desired mechanical properties in an as-cast component.

[0005]It is desirable to have an aluminum casting alloy best suited for
sand and permanent mold casting processes, in which the alloy is highly
resistant to corrosion yet exhibits adequate strength similar to that of
the aluminum alloy for die-casting as disclosed in U.S. Pat. No.
6,733,726 B2. It is also desirable to have an aluminum casting alloy that
is amenable to heat treatment. It is still further desirable to have an
aluminum casting alloy that has a reduced natural affinity for the
aluminium to attack and dissolve the tooling steel, a condition referred
to as soldering.

SUMMARY OF THE INVENTION

[0006]This invention is directed to aluminum alloys having improved
corrosion resistance and excellent strength characteristics for sand and
permanent mold casting processes. Relative to known aluminum alloys, the
aluminum alloys of this invention are characterized by a very low copper
content, a manganese content that is sufficient to input excellent
strength properties, a silicon content that is suitable for fluid flow of
molten alloy into a mold under normal gravity, and an iron content
sufficient to minimize soldering of metallic molds. The lower silicon
content provides for improved mechanical properties, while the lower iron
content provides for increased strength and better creep characteristics
at moderately elevated temperatures and improved ductility.

[0007]These and other features, advantages, and objects of the present
invention will be further understood and appreciated by those skilled in
the art by reference to the following specification and claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008]In accordance with the principles of this invention, an aluminum
casting alloy having improved corrosion resistance and excellent sand and
permanent casting properties includes a relatively low copper content
that is effective to achieve enhanced corrosion resistance, in
conjunction with a relatively lower silicon content for improved
mechanical properties, and a lower iron content to increase tensile
strength and ductility as well as to reduce shrinkage and soldering.

[0009]The aluminum alloys of this invention typically have a silicon
content of from about 4.0 percent by weight to about 8.5 percent by
weight; preferably between about 4.0 to about 7.0 percent by weight.

[0010]Iron is preferably added to the aluminum alloys of this invention to
decrease the tendency for mold sticking or soldering during casting. A
suitable amount of iron is from about 0.2 percent to about 0.8 percent by
weight.

[0011]Conventional aluminum casting alloys typically contain relatively
high amounts of copper in order to improve the machinability, strength,
and hardness of the casting. However, copper reduces resistance to
general corrosion, and therefore, is present in the aluminum alloys of
this invention in relatively low amounts, if at all. In order to achieve
excellent corrosion resistance, the aluminum alloys of this invention
typically contain 0.08 percent copper by weight or less, and more
preferably 0.05 percent or less.

[0012]Most aluminum casting alloys have an aluminum content of about 86
percent by weight or less. For example, the most commonly used aluminum
die casting alloy (alloy 380.0) contains from about 79 to about 83
percent aluminum by weight. The conventional corrosion resistant aluminum
die casting alloys, alloys 360.0 and 413.0, contain from about 85 to
about 86.5 percent aluminum by weight and from about 82 percent to about
84 percent aluminum by weight, respectively. In contrast, the aluminum
alloys of this invention for sand and permanent mold casting have a
relatively high aluminum content, and as a result, exhibit a thermal
conductivity that is about 20 percent greater than that of alloy 380.0.

[0013]Manganese is present in an amount from about 0.25 to about 0.5
percent by weight to enhance strength, and more preferably from about 0.3
to about 0.5, with about 0.40 percent manganese being most preferred.
These levels of manganese have been found to compensate, at least in
part, for the relatively low levels of copper, to enhance strength
properties without significantly adversely affecting corrosion
resistance.

[0014]Magnesium, nickel, zinc and tin may be present in the alloy in
relatively minor amounts, preferably about 1.5 percent or less, more
preferably about 1 percent or less, and even more preferably about 0.6
percent or less.

[0015]Other elements are not desirable, and are preferably present in an
amount of less than 0.5 percent by weight, and more preferably less than
0.03 percent by weight.

[0016]The aluminum alloys of this invention use lower silicon and higher
iron and manganese contents, as compared to known aluminum alloys, to
increase strength and control the grain structure. An advantage of having
higher manganese content is the increase in the sensitivity of heat
treating in obtaining the desired properties. Another advantage of having
higher manganese content is that the manganese combines with magnesium to
insure a greater degree of stability to the alloy. Also, the higher iron
aids in reducing the natural affinity for aluminium to attack and
dissolve tooling steel, a condition referred to as soldering.

[0017]It will be understood by those who practice the invention and those
skilled in the art, that various modifications and improvements may be
made to the invention without departing from the spirit of the disclosed
concept. The scope of protection afforded is to be determined by the
claims and by the breadth of interpretation allowed by law.